1. Field of the Invention
The present invention relates to a method of preventing polymer scale from depositing on the inner wall of a polymerization vessel during the polymerization of a monomer having an ethylenically double bond.
2. Description of Prior Art
In processes of preparing polymers by polymerizing monomers in a polymerization vessel, the problem that polymers deposit on the inner wall and other parts which come into contact with monomers such as a stirring shaft and stirring blades of the polymerization vessel in the form of scale, is known. The deposition of the polymer scale on the inner wall of the polymerization vessel results in disadvantages that the yield of the polymer and the cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into manufactured polymer, thereby impairing the quality of the manufactured polymer; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomers, there is a danger that the workers may be exposed to the unreacted monomers, which may give them some physical disorders.
Various attempts have been made to prevent the polymer scale from depositing on the inner wall of a polymerization vessel. The following art methods are known.
(1) The method disclosed in Japanese Patent Publication (KOKOKU) No. 30845/1970, in which a dye or a pigment is coated on the inner wall of a polymerization vessel.
(2) The method disclosed in Japanese Patent Publication (KOKOKU) No. 24953/1977 in which a polar organic compound or a dye treated with a metal salt is coated on the inner wall.
(3) The method disclosed in Japanese Patent Publication (KOKOKU) NO. 28347/1978 in which a mixture of an electron donor compound and an electron acceptor compound is coated on the inner wall.
(4) The method disclosed in Japanese Patent Publication (KOKOKU) No. 24070/1977 in which an inorganic salt or an inorganic complex is coated on the inner wall.
(5) The method disclosed in Japanese Patent Publication (KOKOKU) Nos. 11561/1982, 3841/1987 and 59246/1985, and Japanese Pre-examination Patent Publication (KOKAI) No. 192413/1982 in which a condensate of a phenol is coated on the wall.
However, in these prior art methods, the effect of preventing the polymer scale formation varies according to polymerization conditions such as the kind of a monomer to be polymerized, the ratio of materials charged in the polymerization vessel, the kind of a polymerization catalyst used, a form of the polymerization and the material constituting the inner wall of the polymerization vessel. As a result, it is difficult to prevent effectively and certainly polymer scale deposition in every case. Particularly, in the case of polymerization of styrene, styrene-butadiene, acrylonitrile-butadiene-styrene or the like in a stainless steel polymerization vessel, serious polymer scale deposits; hence a glass-lined polymerization vessel must be used. However, the glass-lined polymerization vessel has disadvantages that its wall, etc. has a small heat conductivity and poor durability, and that a large polymerization vessel is difficult to produce.